1. Field of the Invention
The present invention relates to a wiring board for electrical tests, and a method of manufacturing the same. By way of example, the electrical tests include the insulation and connection tests of high-density wiring in a printed-wiring circuit board, a circuit board for an integrated circuit or a circuit board for a liquid-crystal display, and the ON-resistance tests of a semiconductor device.
2. Description of the Related Art
As semiconductor devices have been subjected to increased density of integration and density of surface packaging, the tests of the devices and the packaging circuit boards thereof have become very difficult.
In the case of the semiconductor devices, several tensxcx9cseveral hundred of electrodes are laid out on silicon chips of several millimeters square. Further, a semiconductor device having more than one thousand electrodes will be developed. The tests of such devices are extremely difficult. Especially, it is difficult to test a so-called xe2x80x9cbare chipxe2x80x9d which is a silicon chip before being packaged (namely, before being mounted on a lead frame and encapsulated with a resin). Granted that the tests of the bare chip are possible, they are not commonly applied because of complicated test jigs and heavy test expenses.
On the other hand, also in the case of the wiring circuit boards for use in the packaging, the microfabrication of wiring has been promoted. It has been required of the wiring circuit boards to have wiring leads at a pitch of or below 0.1 [mm] and electrodes at a pitch of or below 0.1 [mm] (equal to the electrode pitch of the semiconductor devices). Such wiring circuit boards cannot be tested with regard to insulation and connection by a conventional method which permits the electrodes to be temporarily connected and disconnected, for example, a method in which anisotropic conductive rubber is brought into pressed touch with the electrodes as disclosed in the official gazette of Japanese Patent Application Laid-open No. 3269/1984.
In view of the circumstances stated above, the present invention has for its object to provide a wiring board for electrical tests which facilitates the tests of a semiconductor device, a wiring circuit board or the like (hereinbelow, sometimes termed an xe2x80x9carticle to-be-testedxe2x80x9d).
Another object of the present invention is to provide a method of manufacture which is well suited to the aforementioned wiring board for electrical tests.
A wiring board for electrical tests according to the present invention comprises an insulating substrate, wiring of predetermined pattern which is embedded in the insulating substrate, and bump electrodes which are formed on the wiring and which are respectively brought into contact with corresponding electrodes of an article to-be-tested such as a semiconductor device or a wiring circuit board for packaging use. Herein, the wiring of predetermined pattern serves as lead-out lines which connect the respectively corresponding bump electrodes to measuring instruments arranged outside the wiring board.
The wiring board for electrical tests is manufactured by methods according to the present invention as exemplified below.
One example of the manufacturing method consists in comprising the step of forming wiring of predetermined pattern on a temporary substrate which is electrically conductive and in which a thin nickel layer (0.1xcx9c10 [xcexcm] thick) is formed on an elongate copper foil (20xcx9c100 [xcexcm] thick), the step of embedding the wiring in an insulating substrate, and the step of removing a part of the conductive temporary substrate except the other parts thereof which become bump electrodes that are respectively brought into contact with electrodes of an article to-be-tested. Further, if necessary, this example comprises the step of covering the wiring of predetermined pattern with an insulating layer (a surface passivation layer) so as not to entirely conceal the bump electrodes.
In the above, the step of partly removing the conductive temporary substrate proceeds as follows:
An etching resist of predetermined pattern is formed on those parts of the surface of the copper foil of the temporary substrate which become the bump electrodes. Thereafter, the copper foil is etched with an etchant. Since the etching of the copper foil ends in the thin nickel layer, the wiring of predetermined pattern (made of copper) is not etched. Subsequently, the etching resist is peeled off, and the exposed or denuded part of the thin nickel layer is etched and removed with another etchant.
The formation of the bump electrodes at a high density and at a high accuracy is permitted using that copper foil of the temporary substrate which is as thin as about 20xcx9c30 [xcexcm]. When the copper foil is thicker, the amount of side etching or lateral etching enlarges in etching the copper foil in order to form the bump electrodes, making it impossible to form the high-density and high-accuracy bump electrodes. In the case where the thin copper foil is employed, the bump electrodes as desired can be formed by a method stated below. A plating resist of predetermined pattern is formed on the surface of the thin copper foil. Subsequently, those parts of the foil surface which correspond to the bump electrodes to-be-formed are plated so as to partly increase the thickness of the copper foil. After the plating resist is peeled off, an etching resist is formed on those plated parts of the foil surface which become the bump electrodes, and the thin copper foil is etched and removed with an etchant under this condition. Further, the exposed part of the thin nickel layer is etched and removed with another etchant.
Meanwhile, another example of the manufacturing method according to the present invention consists in comprising the step of forming wiring of predetermined pattern on a temporary substrate, the step of embedding the wiring in an insulating substrate, the step of removing the temporary substrate without damaging the wiring of predetermined pattern formed thereon, the step of depositing an insulating material capable of photo-imaging, on one side of the insulating substrate including the wiring by either coating or lamination techniques, and then subjecting the deposited insulating material to exposure as well as development, thereby forming an insulating layer (a surface passivation layer) which serves as a plating resist, on a part of the one side of the insulating substrate except the other parts thereof which correspond to bump electrodes to-be-formed that are respectively brought into contact with electrodes of an article to-be-tested, and the step of forming the bump electrodes by plating.
In the above, the step of removing the temporary substrate can be so performed that, after a copper foil constituting the temporary substrate is etched and removed with a copper etchant, a thin nickel layer constituting the temporary substrate is etched and removed with a nickel etchant. In addition, the step of forming a photo-image on the insulating layer can be performed using an excimer laser. Besides, the bump electrodes should preferably be formed by performing the plating in excess of the thickness of the photo-imaging material.
Mentioned as an example of the photo-imaging material is a composite which is a photosensitive resist for electroless plating, and which consists of rubber-phenol resin-epoxy resin, an epoxy resin photoinitiator (such as aromatic onium salt) and an aromatic polyazide compound (such as 3,3xe2x80x2-diazidodiphenylsulfone, 4,4xe2x80x2-diazidostilbene, 4,4xe2x80x2-diazidochalcone, and 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diazidobiphenyl).
In the foregoing, there has been described the case where the copper foil and the thin nickel layer of the temporary substrate are removed by etching. It is also allowed, however, to adopt an expedient in which, after the etching and removal of the copper foil, the insulating material capable of photo-imaging is deposited by either coating or lamination techniques and is subjected to exposure as well as development, thereby forming the layer of a plating resist, whereupon the bump electrodes are formed by plating (electroplating). In this expedient, electric power for the electroplating can be fed through the thin nickel layer. After the formation of the bump electrodes, the thin nickel layer is etched and removed.